Cowpea mild mottle virus
A. A. Brunt
Glasshouse Crops Research Institute, Littlehampton, Sussex, England
R. H. Kenten
Cocoa Research Institute, Tafo, Ghana
Described by Brunt & Kenten (1973)
A virus with filamentous particles c. 650 nm long. Seed-borne
in some leguminous hosts and readily sap-transmissible to species in several
families. No known vector. Common in the Eastern Region of Ghana.
Found naturally only in cowpea (Vigna unguiculata
) in which it
usually causes mild leaf mottling but occasionally severe systemic chlorosis
and necrosis (Fig.1
Common in the Eastern Region of Ghana.
Host Range and Symptomatology
Infected 11 of 17 members of the Papilionaceae tested and 10 of 51 other
species within 5 of 19 families (Brunt & Kenten, 1973
- Diagnostic species
- Arachis hypogaea (groundnut). Few necrotic lesions, chlorotic rings or
line patterns in inoculated leaves, soon followed by systemic leaf chlorosis,
leaf rolling and some veinal necrosis. Infected plants are severely stunted.
- Beta vulgaris (beetroot) cv. Detroit. Fawn necrotic local lesions
(Fig.4). No systemic infection.
- Cajanus cajan (pigeon pea). Conspicuous systemic leaf chlorosis and
distortion within 14-28 days; plants are severely stunted.
- Glycine max (soybean) cv. Chippewa. Conspicuous systemic leaf chlorosis
within 14-21 days (Fig.2), occasionally followed by apical necrosis.
- Phaseolus vulgaris (French bean) cv. The Prince. Conspicuous chlorotic
spotting of some systemically infected leaves.
- Nicotiana clevelandii. Inconspicuous systemic leaf chlorosis.
- Theobroma cacao (cocoa) cv. West African Amelonado. Systemic infection
in about half of the seedlings grown from inoculated cocoa beans; immature leaves
develop red vein-banding symptoms but mature leaves have chlorosis along
secondary and tertiary veins (Fig.5).
- Propagation species
- Glycine max and Nicotiana clevelandii are suitable for maintaining
cultures and as sources of virus for purification.
- Assay species
- Chenopodium quinoa is a useful assay host; inoculated leaves produce
numerous chlorotic or necrotic lesions within 12 days (Fig.3).
Transmission by Vectors
Although serologically related to carnation latent virus
, cowpea mild mottle
virus was not transmitted in either the persistent or non-persistent manner by 12
aphid species including Acyrthosiphon pisum, Aphis craccivora, Aphis fabae
and Myzus persicae.
In experiments to investigate whether transmission
is dependent upon a helper virus (Kassanis & Govier, 1971a
cowpea mild mottle virus was not transmitted by Myzus persicae
either on pepper plants infected with potato Y
or pepper veinal mottle
or on Dianthus barbatus
plants infected with carnation latent virus.
Transmission through Seed
Seed-borne (2-90%) in Vigna unguiculata, Glycine max
but not in Nicotiana clevelandii
(Brunt & Kenten, 1973
Transmission by Dodder
Antisera with titres of 1/2048 are readily prepared, and react with homologous
virus preparations to produce flagellar precipitates in precipitin tube tests.
Serologically distantly related to carnation latent virus
, but apparently
unrelated to the following carlaviruses
: pea streak
, red clover vein mosaic
2, chrysanthemum B
, passiflora latent, potato M
, potato S
, narcissus latent
bryony mosaic and a virus from elderberry (Brunt & Kenten, 1973
Stability in Sap
Sap from systemically infected Glycine max
was infective to Chenopodium
after dilution to 10-3
but not 10-4
, after 10 min
at 65°C but not 70°C, and after at least 8 days at 20°C or 20 days at
2°C (Brunt & Kenten, 1973
). Lyophilized sap remains infective for at least
and Nicotiana clevelandii
are the best sources of
virus for purification. Losses of virus due to irreversible aggregation of
particles are minimized by the use of low molarity alkaline buffer. The following
procedure yields 2-5 mg virus/kg of leaf tissue (Brunt & Kenten, 1973
infected leaves at -20°C, then grind in 0.02 M borate at pH 9.5 (2 ml/g tissue),
express the fluid through cotton cloth and centrifuge for 15 min at 10,000
. Shake the supernatant fluid for 5 min with 0.5 vol. chloroform
and, after 1 h at 2°C, centrifuge the mixture for 15 min at 10,000
. Sediment the virus from the aqueous phase by centrifugation for
1 h at 75,000 g
. resuspend the pellets in 0.01 M borate at pH 9.5
and then repeat the cycle of differential centrifugation. Resuspend the virus in
0.01 M borate, freeze it for c.
18 h, thaw and clarify by low speed
centrifugation. Further purification may be achieved by centrifugation through
10-40% linear sucrose density gradients for 2-5 h at 45,000 g
Properties of Particles
Virus preparations contain a single sedimenting component with
of 165 ± 4 S.
A260/A280: 1.14; A260/A246: 1.21 (both after correction for light-scattering).
The virus has straight or slightly flexuous filamentous particles c.
13 x 650 nm (Fig.6
) which readily fragment. In leaf dip preparations
negatively stained particles are occasionally surrounded by a loose external
Particle CompositionNucleic acid: c.
5% of particle weight (estimated spectrophotometrically).
Protein: c. 95% of particle weight (estimated spectrophotometrically); one
type of polypeptide of M.Wt 32,000.
Relations with Cells and Tissues
In ultrathin sections of systemically infected soybean leaves, bundles of
filamentous virus-like particles occur in the cytoplasm (M. James, R. H. Kenten
& A. A. Brunt, unpublished).
NotesCowpea yellow mosaic virus
), the bean strain of tobacco mosaic
(Lister & Thresh, 1955
bean southern mosaic virus
(Lamptey & Hamilton, 1970
also infect cowpeas in West Africa, but cowpea mild mottle virus
differs from these in particle morphology, host plant reactions and other
properties. It also differs in size and/or morphology from other viruses infecting
cowpeas elsewhere, including cowpea aphid-borne mosaic virus
& Conti, 1974
) and peanut mottle virus
) which occur commonly in
cowpea in East Africa. Cowpea mild mottle virus induces leaf symptoms in groundnuts
similar to those found in plants naturally infected with similar viruses in
Kenya (K. R. Bock, personal communication) and Nigeria (R. Hull, personal
communication), but it is not known whether these three viruses are related.
The susceptibility of cocoa (Theobroma cacao) to infection (Brunt &
Kenten, 1973) is especially interesting because infected seedlings produce leaf
symptoms similar to those of an unidentified virus infecting cocoa in the Bompata
area of Ashanti Akim, Ghana (Anon., 1951).
- Anon., Rep. W. Afr. Cocoa Res. Inst. 1949-50: 9, 1951.
- Bock, Ann. appl. Biol. 74: 75, 1973a.
- Bock, Ann. appl. Biol, 74: 171, 1973b.
- Bock & Conti, CMI/AAB Descriptions of Plant Viruses 134, 4pp., 1974.
- Brunt & Kenten, Ann. appl. Biol. 74: 67, 1973.
- Chant, Ann. appl. Biol. 47: 565, 1959.
- Kassanis & Govier, J. gen. Virol. 10: 99, 1971a.
- Kassanis & Govier, J. gen. Virol.13: 221, 1971b.
- Lamptey & Hamilton, Phytoprotection 51: 151, 1970.
- Lister & Thresh, Nature, Lond. 175: 1047, 1955.
Severe chlorotic mottle in systemically infected Vigna unguiculata
Systemically infected Glycine max leaf.
Inoculated Chenopodium quinoa leaf.
Inoculated Beta vulgaris leaf.
Systemically infected Theobroma cacao leaf.
Virus particles in phosphotungstate. Bar represents 200 nm.
Virus particles with external spirals from V. unguiculata. Bar
represents 200 nm.